Author Topic: A knot by Design  (Read 26057 times)

knot4u

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Re: A knot by Design
« Reply #30 on: February 11, 2011, 01:53:56 AM »
Try it for ourself and let me know what you find, but also, please let me know why you feel the hitch is 'fundamentally flawed'

I think the KC Hitch is fundamentally flawed because the hitch must stretch out into relatively long ellipsoid coils in order for it to grip.  If you don't see that as a flaw, then you may rest assured that the problem lies with me and not with the knot.

Yes, I thought that a most provocative & unsupportable assertion,
myself --compounded by invoking the "Gleipnir pipe hitch" as anything
to be proud of!  One can envision a simple sort of Tug-of-War test on
these.  KC will take --indeed, nearly requires-- an initial yielding of
grip as it extends & tightens (so, too, Blake's/ProhGrip & Klemheist
--any coil-away structure, really),
but then it does tighten.  As does the Icicle, another coil-away hitch.

And that Gleipnir structure in that circumstance should prove
especially ineffective at its own nipping!

I guess it comes down to this:  My testing has led me to different conclusions.  However, we all may rest assured because I'm the one tying my knots, and you're the one tying your knots.

;)
« Last Edit: February 11, 2011, 01:57:25 AM by knot4u »

Dan_Lehman

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Re: A knot by Design
« Reply #31 on: February 11, 2011, 08:17:11 AM »
I think the KC Hitch is fundamentally flawed because the hitch must stretch out into relatively long ellipsoid coils in order for it to grip.  If you don't see that as a flaw, then you may rest assured that the problem lies with me and not with the knot.

Or, rather, it might speak to the circumstances : in the large contrasting
sizes of object & line shown by Derek, it doesn't stretch out so much;
as those sizes become less different, the gripping is more a challenge
and it will stretch more.  So, if not fundamentally "flawed," it is more
limited in practical application, then, perhaps.

So, the conditions (perhaps a variety) for the hitch-off Tug-o-War
yet need to be specified!


--dl*
====

DerekSmith

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Re: A knot by Design
« Reply #32 on: February 11, 2011, 07:16:47 PM »
Hi K4u,

Thanks for the reply.  I think we are moving forward, in that your reply suggests that you see the fundamental flaw as the need for the hitch to " stretch out into relatively long ellipsoid coils in order for it to grip"..  Would I be correct in assuming that it is the amount of stretch that you see as the flaw?  If my assumption is correct, then perhaps I have a basis to work from.

The definition of a knot that I choose to work with is that a knot is a Force Machine - physically simplistic, technically highly complex (it follows from this definition that cordage constructions that are not involved in force processing are either tangles or Decoratives , but that is the subject of another discussion).  It goes without saying, that knots do not work by magic,  they work with tensile and lateral forces, compressive forces and of course, putting it all to work - FRICTION.  All cordage has a modulus of elasticity - some low, some surprisingly high, and as a tensile force is applied, the cords will stretch and slightly narrow under the applied load.

When a load is applied to a bend, the geometry of the knot applies the laterally generated forces to create internal grip of cord against cord.

When a load is applied to a hitch, the geometry of the knot applies the laterally generated forces to create grip against its 'host' object.

Paraphrasing that - load causes extension and creates force vectors, geometry creates tangential pressure and from this, friction with(against) the 'host' object.

Taking then the group of knots you have cited, essentially they all comprise a bunch of turns around the 'host'.  None of them are drawn particularly tight (there is no 'Truckers Hitch' type elements in their make up), consequently they can all be relatively easily slid along the host.

So now we put them to work - in order for these round turns to grip, they need to develop tangential pressure in order to engage the coefficient of friction, and they all do it in the same manner - when a load is applied at right angles to the coils, they are subject to infinite leverage, so they move along the host in the direction of the load.  If we are lucky one side moves while the opposite side stays put - this causes the cord turns to elongate into an ovoid shape and this stretching puts the cords under tension and the tension gives rise to the tangential pressure which builds the friction.  The round turns continue to extend (become longer ovals) until the friction generated becomes great enough to hold the dragging force.

The problem with the coils opening, is that as the angle increases beyond 90 degrees, then the vector starts to express not only a compressive component at the back of the coils, but also it generates an increasing vector in line with the drag force.  In low friction situations, this force is eventually great enough to force the back of the loops to slide forwards, and the moment this happens, the knot has failed.

This weakness is what the KC was designed to avoid.  In the KC, there is no connection between the drag input and the back of the hitch.  The only way a drag vector can reach the back of the hitch is if the friction is so low, that every turn is pulled open - then the KC will fail - this is why the stipulation is made that there should be sufficient turns that the last two do not open - these are the 'anchor' or 'root' of the hitch - if they have not been pulled open, then no slip force has reached the back of the hitch and the oval turns have generated all the necessary tension to create the required tangential force and hence frictional grip.

So now we have it - the fact that the first turn (or two or three... turns) have progressively opened is not a flaw at all - it is the reason why the KC has to hold while other hitches which are flawed by having the dragging force transmitted to every coil simultaneously will fail (in low friction situations).

Derek

knot4u

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Re: A knot by Design
« Reply #33 on: February 11, 2011, 10:29:46 PM »
The problem with the coils opening, is that as the angle increases beyond 90 degrees, then the vector starts to express not only a compressive component at the back of the coils, but also it generates an increasing vector in line with the drag force.  In low friction situations, this force is eventually great enough to force the back of the loops to slide forwards, and the moment this happens, the knot has failed.

This weakness is what the KC was designed to avoid.  In the KC, there is no connection between the drag input and the back of the hitch.  The only way a drag vector can reach the back of the hitch is if the friction is so low, that every turn is pulled open - then the KC will fail - this is why the stipulation is made that there should be sufficient turns that the last two do not open - these are the 'anchor' or 'root' of the hitch - if they have not been pulled open, then no slip force has reached the back of the hitch and the oval turns have generated all the necessary tension to create the required tangential force and hence frictional grip.

So now we have it - the fact that the first turn (or two or three... turns) have progressively opened is not a flaw at all - it is the reason why the KC has to hold while other hitches which are flawed by having the dragging force transmitted to every coil simultaneously will fail (in low friction situations).

Derek

The weakness you mentioned is theoretical.  If I make the stipulation (like you did) that at least the top two coil remain together, then the hitches I mentioned have not failed on me.  Also, let's compare apples to apples. The KC Hitch in the original post would need to be compared to a Well Pipe Hitch (ABOK #504) having 8 coils because that's how many coils your KC Hitch has.  If you manage to slip a Well Pipe Hitch having 8 coils tightly dressed, then please share the parameters you used before we get caught up in too much theory here.  At least try that hitch out before you further explain this theoretical weakness.  I just got done testing that hitch on a slick vertical pole.  It's a robust diesel.

For reference, here are the hitches I'm comparing to the KC Hitch:
http://igkt.net/sm/index.php?topic=1889.0

However, let's back up.  The fundamental operation of the KC Hitch is vastly different than the hitches I mentioned.  It's awkward comparing fine details of the knots because, before we get to the details, the fundamentals are so hugely different.  The KC Hitch and the hitches I mentioned can co-exist because they each excel in different categories.

In the hitches I mentioned, a feature (probably the strongest feature) is that the tangential forces against the pole increase proportionally as the load increases.  Accordingly, if the hitch holds with a mild load, it's a fair assumption that the hitch will hold with a heavier load (given the hitch undergoes little more deformation).

In contrast, the KC Hitch is a bit more complex with how the force against the pole increases.  The KC Hitch relies on its elongation AND overlaps to increase the pressure against the pole.  The top of the hitch must initially be fairly tight, AND the top of the hitch only increases in tightness as the forces work their way up through the coils and overlaps to make the top of the KC Hitch tight.  In fact, the KC Hitch does not even rely much on the top coils.  That feature may be preferable on a cone-shaped pole where the standing end is pulled in the direction of the narrow part of the pole.  (Just guessing, I have not tested this application.)

A weakness of the KC hitch is the overlaps, which ironically are necessary for the KC Hitch to work.  Note that you have displayed relatively thin rope on a relatively thick pole.  I contend that's the ideal and only recommended use for the KC Hitch.  In contrast, if we have relatively THICK rope on a relatively THIN pole, then suddenly the overlaps compromise security, but again the overlaps are necessary.  What are the relative rope dimensions at which we no longer recommend the KC Hitch?  Take your guess, and make sure the person is not asking you about a critical application.  Note, this issue is less of a concern (or non-existent) with a Well Pipe Hitch.

To recap, the KC Hitch and the hitches I mentioned can co-exist because they each excel in different categories.  I might prefer the KC Hitch on a cone-shaped pole where the standing end is pulled in the direction of the narrow part of the pole.  (Just guessing, I have not tested this application.)  I would prefer the other hitches I mentioned for most (or all) other applications.
« Last Edit: February 12, 2011, 12:51:01 AM by knot4u »

Dan_Lehman

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Re: A knot by Design
« Reply #34 on: February 12, 2011, 05:22:21 AM »
For reference, here are the hitches I'm comparing to the KC Hitch:
http://igkt.net/sm/index.php?topic=1889.0

WOW, for a guy giving so much voice to locking threads,
going back to edit in a new knot-image into the OP of a June
2010 thread in 2011 wins a prize!?  Good way to make the
replies look like they're missing part of the post.

Quote
 I might prefer the KC Hitch on a cone-shaped pole where the standing end is pulled in the direction of the narrow part of the pole.  (Just guessing, I have not tested this application.)  I would prefer the other hitches I mentioned for most (or all) other applications.

I don't know, it seems that with each extension degree KC is
surrounding a diminishing diameter and so would need to
extend farther and ... --not a good case for it.  (I don't know
of anything with a much of a taper on it to test --shovel handle's
taper is slight.)

--dl*
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knot4u

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Re: A knot by Design
« Reply #35 on: February 12, 2011, 06:29:59 AM »
For reference, here are the hitches I'm comparing to the KC Hitch:
http://igkt.net/sm/index.php?topic=1889.0

WOW, for a guy giving so much voice to locking threads,
going back to edit in a new knot-image into the OP of a June
2010 thread in 2011 wins a prize!?  Good way to make the
replies look like they're missing part of the post.

Yes, that's lame on my part.  Further, I gutted over 10 posts from that thread.  The thread is now mangled.  The good news is you only need my original post.  :)